In the manufacture of paper products, it is desirable to accurately and reliably measure the rate at which liquid penetrates through a paper sample. Such measurements are generally made using a device called a "penetrometer," which typically operates by measuring the time needed for a colored 18 liquid (hereinafter referred to generically as "ink") to penetrate through a sample by monitoring the light reflectance of 20 the opposite side of the sample to detect appearance of the penetrated ink. U.S. Pat. No. 3,512,003, for example, discloses such a penetrometer. Another well known penetrometer is the Hercules Sizing Tester, as described in "Evaluation of the Hercules Sizing Tester," TAPPI Joint Papermakers/Testing Conf., 131-6, Sep. 25-27, 1973.
Conventional ink penetrometers--such as the '003 device--deliver ink to the sample-under-test by means of a paddle or well which is raised by a pneumatic system so that the ink contacts the sample to begin the test. Unfortunately, this pneumatic system is difficult to calibrate and maintain, and yet its calibration and maintenance is critical to the accuracy of the penetrometer.
In view of the above, one object of the present invention is a highly accurate and reliable ink penetrometer.
Another object of the invention is a penetrometer with single push-button operation, including automatic sampling and lock-in of the 100% reflectance value of the sample prior to the test, automatic control of a run timer, single fill pump action, automatic drain and automatic status display.
Still another object of the invention is a penetrometer having reduced maintenance requirements.
Yet another object of the invention is a penetrometer in which fresh, uncontaminated ink is used for each test, and which requires only occasional cleaning of the ink paddle.
Another object of the invention is a penetrometer which utilizes modern, solid state control and measurement circuitry.
Still another object of the invention is a penetrometer having an improved ink delivery system.
Yet another object of the invention is a penetrometer having a compact photohead which employs modern, fiber optic technology.
Still another object of the invention is a penetrometer including means for outputting and/or displaying, in real time, the ratio of current reflectance to an initial, locked-in reflectance value as the testing cycle progresses.
Another object of the invention is a penetrometer in which the light source and detector are separated from each other, and both are separated from the chemical environment of the fluid, thereby increasing the stability and durability of the sensors.